1. Field of the Invention
The present invention relates to an apparatus for plating wafers for semiconductors, more particularly to a cup-type plating apparatus in which the wafer is placed on an opening of a plating tank and is subjected to plating.
2. Description of the Related Art
Recently, various kinds of plating, for example, formation of a bump, are performed in the manufacturing process of wafers for semiconductors. A cup-type plating apparatus is known as one of the apparatuses for plating the wafer.
In this cup-type plating apparatus, a plating solution is supplied to a wafer, which is placed on a wafer support provided along an opening at the top of a plating tank, via a solution-supply port provided at the bottom of the plating tank by an upward-moving stream, and flows out of a solution-outlet port provided for the plating tank; thus, plating is performed while bringing the plating solution into contact with a surface of the placed wafer to be plated.
In the cup-type plating apparatus, the plating solution supplied toward the surface of the wafer to be plated, by the upward-moving stream makes the plating solution into contact with the surface to be plated in a flowing state in which the solution spreads out from the center toward the periphery of the surface; thus, uniform plating can be performed on the entire surface to be plated. Since plating can be performed in such a manner that the wafer to be placed on the wafer support of the plating tank is successively replaced, the apparatus is widely used as a suitable apparatus for small-lot production or automatization of plating process.
In the conventional cup-type plating apparatus, the plating solution supplied from the solution-supply port by the upward-moving stream is flowed out from the solution-outlet port provided over the plating tank in a state in which the plating solution is directly exposed. Therefore, in this cup-type plating apparatus, a mist of the plating solutions may be generated due to the plating solution which flowed out of the plating tank, and may adhere to the surface (the rear of the surface to be plated) of the wafer placed on the wafer support. Conventionally, since the contaminant on the surface of the wafer due to the mist of the plating solutions is removed in a later cleaning process, it has not been perceived to pose a particular problem.
The development of plating process in which more wafers can be speedily processed is in progress as a demand for the wafers rapidly increases. As an example, the supply of the plating solution or the current density for plating is increased for realizing high-speed plating. When the supply of the plating solution is increased, the mist of the plating solutions is also increased, and the contaminant on the surface of the wafer resulting from the mist is more prominent than it was; thus, the necessity for afterward careful cleaning arises.
Since a large number of wafers are plated at the same time, a plating unit having a plurality of cup-type plating apparatuses may be manufactured, thereby realizing an efficient plating process. In this case, a large amount of the mist of the plating solutions is likely to be generated at a time due to the plating solution flowing out of a plurality of the plating tanks, and consequently, the contaminant on the surface of the wafer is likely to be increased.
Furthermore, the recent wafer manufacturing process is almost automated; wherein the wafers are successively moved in the processes, and in many cases, after completion of plating, the cleaned and dried wafers are moved to a clean room, and a downstream process is then performed. Therefore, when no measures against the mist of the plating solutions is taken, for instance, when a large amount of mist of the plating solutions exists in the plating process, it may leak into the clean room to generate contamination in the clean room; and, accordingly, it is not preferable for manufacturing wafers.
In the recent wafer-manufacturing process, because of the foregoing reasons, a cup-type plating apparatus in which the contamination on the surface of a wafer due to a mist of plating solutions can be prevented as much as possible is strongly required. Accordingly, it is an object of the present invention to provide a technique in which the conventional cup-type plating apparatus is improved, and the contamination on the surface of the wafer due to the mist of the plating solutions can be prevented.
In order to achieve the above object of the present invention, a plating solution is supplied to a wafer which is placed on a wafer support provided along an opening at the top of a plating tank from a solution-supply port provided at the bottom of the plating tank by an upward-moving stream; the plating solution is made to flow out of a solution-outlet port provided for the plating tank; and plating is performed while the plating solution is brought into contact with a surface of the placed wafer, which is to be plated; wherein the solution-outlet port has a solution-outlet path in which the discharged plating solution is isolated from the outer space.
In the cup-type plating apparatus according to the present invention, since the plating solution flowing out of the plating tank is in a state isolated from the outer space, that is, a state separated from the space in which the surface (the rear of the surface to be plated) of the wafer placed on the wafer support is exposed, the contamination on the surface of the wafer due to the mist of the plating solutions can be prevented.
The structure of the solution-outlet path according to the cup-type plating apparatus in the present invention is not particularly limited as long as the it is a structure in which the plating solution flowing out of the solution-outlet port which is provided for the plating tank is isolated from the outer space, that is, it does not directly come into contact with the outer space. For example, an outlet pipe may be provided as the solution-outlet path in such a manner that it is connected to the solution-outlet port provided for the plating tank; alternatively, a solution-outlet path may be provided in which a cover case capable of covering the outer periphery of the plating tank, so that the plating solution flowing out of the solution-outlet port can be isolated from the outer space.
In the cup-type plating apparatus according to the present invention, preferably, the solution-outlet path passes through the interior of the wall of the tank from the solution-outlet port provided on the side of the inner periphery of the wall of the tank, which constructs the plating tank. Thus, the solution-outlet path in which the plating solution can pass through is provided in the interior of the wall of the tank, which constructs the plating tank, so that the plating solution flowing out of the solution-outlet port provided on the inner periphery of the wall of the tank is isolated from the outer space. Accordingly, a space for providing the solution-outlet path on the outside of the plating tank is not required, and the cup-type plating apparatus itself can be made compact. It is particularly effective when constructing a plating unit having a plurality of the cup-type plating apparatuses.
In order to reliably prevent the contamination on the surface of the wafer due to the mist of the plating solutions, preferably, a shutting means capable of closing the opening of the plating tank is provided. In the cup-type plating apparatus, while plating is performed in such a manner that the wafer which is placed on the wafer support provided along the opening of the plating tank is successively replaced, the opening of the plating tank is in an opened state during replacement. At this time, the mist of the plating solutions leaks a little from the opening into the outer space. When replacing of the wafer is completed in a relatively short time, that is, the time of opening the opening is short, it has little effect on the contamination on the surface of the wafer; however, when replacing of the wafer requires a long time, that is, when the opening is opened for a long time, the amount of mist of the plating solutions which leaks out is increased, and accordingly, there is a fear that it exerts an influence on the contamination on the surface of the wafer. Therefore, when the opening of the plating tank is closed when necessary by the shutting means capable of closing the opening of the plating tank, the contamination on the surface of the wafer due to the mist of the plating solutions can be further reliably prevented.